1. Field of the Invention
The present invention relates to a method and apparatus for calibrating an optical probe, and more particularly to a method and apparatus for calibrating an optical probe using a disposable calibration body.
2. Description of Related Art
Various optical probes are available for investigating properties of animal tissue in vivo and in vitro. In spectroscopy, various illuminating wavelengths are applied to the tissues of an animal body, typically through the probes but also through ambient light or through separate light sources. The probes receive optical activity resulting from application of the illuminating energy for detecting properties of the animal body. Typically, a probe is part of a diagnostic or screening system that includes electromagnetic sources for generating the illuminating energy, filters or spectrum analyzers for isolating wavelengths of interest, and computers for processing the wavelengths of interest to determine the tissue properties of interest.
System calibration is performed to minimize the impact of system variations and perturbations and to ensure the most accurate determinations possible. Calibration reduces the effects of variations in the dimensions and optical characteristics of different probes, compensates for drift and other instabilities over time in the electronic detection system caused by various environmental factors and aspects of the systems, including heat, humidity, voltage fluctuations, component aging, cable displacements, accumulated contamination, and the like, and compensates for various system and component failures.
One calibration technique used in fluorescent spectroscopy involves dipping the probe into a fluorescent solution such as Rhodamine, or placing the probe directly against a calibration cell containing the fluorescent solution. While generally effective for calibration purposes, the use of such liquids has several disadvantages which limit their usefulness for operational deployment in a clinical setting. Some of the fluorescent liquids raise safety and usage issues of toxicity, leakage, spillage, and the like. Some of the fluorescent liquids have a short lifetime and must be replaced on a preventive maintenance schedule or after each use. Where the probe is placed against a glass or plastic vial which contains the fluorescent liquid, measures must be taken to eliminate interference reflection and interaction with room lighting. Moreover, the result of calibrations with vials can be operator-dependent. Where the probe is immersed in the fluorescent liquid, calibration in the exam room involves awkward procedures.
Accordingly, methods and apparatus are desired that do not have the disadvantages of the liquid and vial calibration procedures.